/**
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.inject.internal;

import com.google.common.base.Objects;
import com.google.common.base.Preconditions;
import com.google.common.cache.Cache;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.RemovalCause;
import com.google.common.cache.RemovalListener;
import com.google.common.cache.RemovalNotification;
import com.google.common.collect.LinkedHashMultiset;
import com.google.common.collect.Maps;
import com.google.common.collect.Multiset;
import com.google.common.collect.Sets;
import com.google.inject.Key;
import com.google.inject.internal.util.SourceProvider;

import java.util.Map;
import java.util.Set;

/**
 * Minimal set that doesn't hold strong references to the contained keys.
 *
 * @author dweis@google.com (Daniel Weis)
 */
final class WeakKeySet {

    private Map<Key<?>, Multiset<Object>> backingMap;

    /**
     * This is already locked externally on add and getSources but we need it to handle clean up in
     * the evictionCache's RemovalListener.
     */
    private final Object lock;

    /**
     * Tracks child injector lifetimes and evicts blacklisted keys/sources after the child injector is
     * garbage collected.
     */
    private final Cache<State, Set<KeyAndSource>> evictionCache = CacheBuilder.newBuilder().weakKeys().removalListener(new RemovalListener<State, Set<KeyAndSource>>() {
        @Override
        public void onRemoval(RemovalNotification<State, Set<KeyAndSource>> notification) {
            Preconditions.checkState(RemovalCause.COLLECTED.equals(notification.getCause()));

            cleanUpForCollectedState(notification.getValue());
        }
    }).build();

    /**
     * There may be multiple child injectors blacklisting a certain key so only remove the source
     * that's relevant.
     */
    private void cleanUpForCollectedState(Set<KeyAndSource> keysAndSources) {
        synchronized (lock) {
            for (KeyAndSource keyAndSource : keysAndSources) {
                Multiset<Object> set = backingMap.get(keyAndSource.key);
                if (set != null) {
                    set.remove(keyAndSource.source);
                    if (set.isEmpty()) {
                        backingMap.remove(keyAndSource.key);
                    }
                }
            }
        }
    }

    WeakKeySet(Object lock) {
        this.lock = lock;
    }

    public void add(Key<?> key, State state, Object source) {
        if (backingMap == null) {
            backingMap = Maps.newHashMap();
        }
        // if it's an instanceof Class, it was a JIT binding, which we don't
        // want to retain.
        if (source instanceof Class || source == SourceProvider.UNKNOWN_SOURCE) {
            source = null;
        }
        Multiset<Object> sources = backingMap.get(key);
        if (sources == null) {
            sources = LinkedHashMultiset.create();
            backingMap.put(key, sources);
        }
        Object convertedSource = Errors.convert(source);
        sources.add(convertedSource);

        // Avoid all the extra work if we can.
        if (state.parent() != State.NONE) {
            Set<KeyAndSource> keyAndSources = evictionCache.getIfPresent(state);
            if (keyAndSources == null) {
                evictionCache.put(state, keyAndSources = Sets.newHashSet());
            }
            keyAndSources.add(new KeyAndSource(key, convertedSource));
        }
    }

    public boolean contains(Key<?> key) {
        evictionCache.cleanUp();
        return backingMap != null && backingMap.containsKey(key);
    }

    public Set<Object> getSources(Key<?> key) {
        evictionCache.cleanUp();
        Multiset<Object> sources = (backingMap == null) ? null : backingMap.get(key);
        return (sources == null) ? null : sources.elementSet();
    }

    private static final class KeyAndSource {
        final Key<?> key;
        final Object source;

        KeyAndSource(Key<?> key, Object source) {
            this.key = key;
            this.source = source;
        }

        @Override
        public int hashCode() {
            return Objects.hashCode(key, source);
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj) {
                return true;
            }

            if (!(obj instanceof KeyAndSource)) {
                return false;
            }

            KeyAndSource other = (KeyAndSource) obj;
            return Objects.equal(key, other.key) && Objects.equal(source, other.source);
        }
    }
}
